JavaScript Optimization: 10 Proven Techniques for Faster Code

Photo by NASA on Unsplash

JavaScript is a cornerstone of web development, hence its performance significantly impacts the overall speed and user experience of your website. This post will dive into ten crucial techniques to optimize JavaScript performance, covering both foundational and advanced practices.

1. Use Local Variables

Reducing the use of global variables can enhance your JavaScript performance as they remain in the memory throughout the lifecycle of the application. Using local variables within functions frees up memory as soon as the function execution completes.

// Instead of using global variables
var globalVar = 'I am Global';

// Use local variables inside functions
function useLocalVar() {
  var localVar = 'I am Local';
}

2. RequestAnimationFrame for Animations

JavaScript animations can be optimized using requestAnimationFrame instead of setInterval or setTimeout as it ensures smoother and synchronized animations.

function animate() {
  // Your animation logic
  requestAnimationFrame(animate);
}
animate();

3. Loop Optimization

Avoid computing the length of an array in each iteration of a loop. Instead, calculate the length before the loop begins.

var arr = [1, 2, 3, 4, 5];

// Cache the length first
var len = arr.length;
for (let i = 0; i < len; i++) {}

4. Use Map or Set for Lookup

For large data sets, using an array’s indexOf method to check the presence of an item can be slow. A Map or Set can significantly speed up lookup operations.

let mySet = new Set(['a', 'b', 'c']);

// Fast lookup
console.log(mySet.has('a'));  // true

5. Use Lazy Loading

Lazy loading is a technique that delays loading of non-critical resources at page load time. Instead, these resources are loaded when they are needed, reducing the initial load time.

// Example of lazy loading an image
<img data-src="image.png" class="lazyload">

6. Avoid Using eval()

The eval() function in JavaScript can execute arbitrary code, which makes it a serious security risk. It's also slower as the JavaScript compiler cannot optimize the code.

// Avoid using eval()
// var result = eval('2 + 2');

// Do this instead
var result = 2 + 2;

7. Use Web Workers for Long Tasks

Web Workers run in an isolated thread. As a result, the ‘main thread’ can run without being blocked, which keeps your site responsive.

let worker = new Worker('worker.js');

8. Use const and let over var

const and let, introduced in ES6, are block-scoped and often more predictable than var. Moreover, const can improve performance by allowing JavaScript engines to optimize the code.

// Instead of var
// var x = 1;

// Use let or const
let x = 1;

9. Reduce DOM Manipulations

Accessing and changing the DOM can be slow. Minimize DOM manipulations by caching DOM references and batch updating changes.

// Cache DOM reference
let myElement = document.getElementById('myElement');

// Now use myElement without querying the DOM again

10. Compress and Minify JavaScript Files

Compressing and minifying your JavaScript files can significantly reduce their size, leading to faster load times.

# Example using UglifyJS
uglifyjs script.js -o script.min.js

If you enjoyed the article and would like to show your support, be sure to:

👏 Applaud for the story (50 claps) to help this article get featured

👉Follow me on Medium

Check out more content on my Medium profile